fox32rom: Don't use the stack pointer for the event stack

Previously this used a very hacky way to push and pop events on the
event stack. This especially caused issues since it disabled and
enabled interrupts, and these routines are called in an interrupt
handler, which breaks things in some cases :p

event.asm

@@ -37,21 +37,38 @@ wait_for_event:
 ; outputs:
 ; none
 push_event:
-    icl
     push r6
-    mov r6, rsp
-    mov rsp, [event_stack_pointer]
-    push r0
-    push r1
-    push r2
-    push r3
-    push r4
-    push r5
-    mov [event_stack_pointer], rsp
-    mov rsp, r6
-    pop r6
-    ise
 
+    mov r6, [event_stack_pointer]
+    ; TODO: check to make sure we don't accidentally clobber the system stack by pushing too many events
+
+    ; push r0
+    sub r6, 4
+    mov [r6], r0
+
+    ; push r1
+    sub r6, 4
+    mov [r6], r1
+
+    ; push r2
+    sub r6, 4
+    mov [r6], r2
+
+    ; push r3
+    sub r6, 4
+    mov [r6], r3
+
+    ; push r4
+    sub r6, 4
+    mov [r6], r4
+
+    ; push r5
+    sub r6, 4
+    mov [r6], r5
+
+    mov [event_stack_pointer], r6
+
+    pop r6
     ret
 
 ; pop an event from the event stack
@@ -66,21 +83,37 @@ pop_event:
     cmp [event_stack_pointer], event_stack_pointer
     ifz jmp pop_event_empty
 
-    icl
     push r6
-    mov r6, rsp
-    mov rsp, [event_stack_pointer]
-    pop r5
-    pop r4
-    pop r3
-    pop r2
-    pop r1
-    pop r0
-    mov [event_stack_pointer], rsp
-    mov rsp, r6
-    pop r6
-    ise
 
+    mov r6, [event_stack_pointer]
+
+    ; pop r5
+    mov r5, [r6]
+    add r6, 4
+
+    ; pop r4
+    mov r4, [r6]
+    add r6, 4
+
+    ; pop r3
+    mov r3, [r6]
+    add r6, 4
+
+    ; pop r2
+    mov r2, [r6]
+    add r6, 4
+
+    ; pop r1
+    mov r1, [r6]
+    add r6, 4
+
+    ; pop r0
+    mov r0, [r6]
+    add r6, 4
+
+    mov [event_stack_pointer], r6
+
+    pop r6
     ret
 pop_event_empty:
     mov r0, empty_event_type